1. Field of the Invention
The present invention relates to an interface system for connecting a control circuit to a host computer system by a plurality of signal lines.
2. Description of the Prior Art
In a magnetic disc system using a floppy disc, for example, a known interface system has a wiring arrangement as shown in FIGS. 1 and 2. In FIG. 1 illustrating a radial chain drive system, interface circuits 4a-4d are connected to a host computer 1 through individual signal cables 11a-11d which correspond respectively to a set of signals from the host computer 1 to the respective interface circuits.
In FIG. 2 illustrating a parallel drive system, a set of signals from a host computer 1 are supplied commonly through a single signal cable 12 to a plurality of interface circuits 14a-14d, each having a select jumper connector 6 having jumper terminals SELECT 1-SELECT 4, and selectively drive these interfaces in accordance with a selected terminal of SELECT 1-SELECT 4.
The interface circuits 14a-14d in FIG. 2, which are driven in a parallel fashion, are shown in more detail in FIG. 3. In the figure, the interface circuits 14a-14d are generally designated by reference numeral 14, for the sake of simplicity.
In FIG. 3, the output signals from the host computer 21, for example, known outputs such as SELECT 1-SELECT 4, WRITE DATA, WRITE GATE, DIRECTION IN, STEP, MOTOR ON, SIDE SELECT, HEAD LOAD, are respectively connected to signal lines 9a-9k and 9a-9h, through signal lines 13i-13k and 13a-13h and an interface connector 5. The output signals on the signal lines 9a-9h are supplied to a control unit 3 for controlling a magnetic disc unit 20. The output signals SELECT 1-SELECT 4 on the signal lines 9i-9k and 9a are respectively connected to the select terminals SELECT 1-SELECT 4 of the jumper connector 6. The connector 6 of each of the interface circuits 14a-14d has a predetermined connection of the terminals by a short-circuiting pin, as shown in FIG. 2. This connection allows the host computer 21 to select any of the interface circuits 14a-14d by the signals SELECT 1-SELECT 4.
To each of the signal lines 9a-9h is connected one terminal of a resistor element 2a-2h respectively of a terminal resistor array 2. The other terminals of the resistor elements 2a-2h have a common connection to a power source of +5 V, for example. This connection controls the current in an interface buffer of the host computer 21 and provides impedance matching to reduce a reflecting wave in the interface cable 12.
In the parallel drive system shown in FIG. 2, from the standpoint of impedance matching, the terminal resistor array 2 is connected to only the interface circuit 14d remote from the host computer 21, while the resistor arrays 2 in the remaining interface circuits 14a-14c are removed.
If the resistor elements 2a-2h are used in the circuit arrangement shown in FIG. 3, a signal transmitting through the resistor 2a into the signal line 9a is transmitted into the signal line 9b, since the resistor elements 2a and 2b are connected in series between the signal lines 9a and 9b. Similarly, a signal passing through the signal line 9a also flows through the resistor elements 2a and 2c-2h into the respective signal lines 9c-9h. Therefore, the terminal resistor array 2 must be removed if not necessary, as described above.
To this end, the interface circuits 14a-14d must be so designed as to facilitate an easy removal of the terminal resistor array 2 therefrom.
For this reason, a manufacture of such an interface system delivers the interface systems having the terminal resistor arrays 2 inserted into the socket of each of the ICs containing the interface circuits. When a user uses the interface systems, some of the terminal resistor arrays 2 remain inserted into the IC sockets, as in the interface circuit 14d in FIG. 2, and some of the terminal resistor arrays 2 are removed from the sockets, as in the interface circuits 14a-14c.
As described above, the conventional arrangement needs the IC sockets for detachably connecting the resistor arrays 2. Use of such a socket increases the manufacturing cost. It is required to design the interface systems in such a way that a user can easily remove the terminal resistor array from the socket.